1. Field of the Invention
The present invention is related to a zoom lens mounting device.
2. Description of the Prior Art
In an encasing barrel, there are fitted a sliding movement guide sleeve having longitudinally straight grooves for moving an optical lens system straight within the barrel in response to the zooming operation of a zoom control ring to vary the zoom ratio of the movable parts of the optical lens system and a cam sleeve provided with cam grooves for moving a front lens system and a rear lens system of the lens optical system along predetermined curves to obtain an optical distance between the front and rear lens system. The lens holding rings are moved in engagement with the above-described longitudinal straight grooves and cam grooves at the intersections thereof. The relative angular position of the guide and cam sleeves must be adjusted by taking into account the distance from the rear lens group of the lens optical system to the film plane in the camera (the so-called back focal length).
In the prior art, the method of adjusting the reference position of the movement of lens holding rings within the barrel is to make use of a washer having a certain thickness inserted between the stationary support sleeve of the interchangeable lens and the mount member thereof so that the abovedescribed distance is established. (This distance adjusting washer will be hereinafter referred to as a "focus washer").
FIG. 1 shows a conventional adjusting method using such focus washer.
Element 1 is a male mount member on the interchangeable lens side, and the mount member is fixed to a fixing sleeve 3 of the lens barrel by tightening and fixing members (not shown).
The fixing sleeve 3 is provided with straight grooves 3a, 3b along the direction of the optical axis.
Element 4 is a cam sleeve rotatably fitted on the outer periphery of the fixing sleeve about the optical axis and cooperative with a control ring (not shown). In the cam sleeve, there are provided cam grooves 4a, 4b formed on the periphery of the cam sleeve as shown by dashed lines. Elements 5, 6 are holding rings for holding a first lens group 9 and a second lens group 10 in an axially movable manner, being fitted in the inner diameter of the fixing sleeve 3.
Elements 7, 8 are pins outwardly extending from the holding rings 5, 6 through the straight grooves 3a, 3b of the fixing sleeve 3 into the cam grooves 4a, 4b of the cam sleeve 4. In FIG. 2, the intersections of the straight grooves 3a, 3b and the cam grooves 4a, 4b at which the pins 7, 8 stand are defined as the movement reference position.
With the construction described above, when the control ring (not shown) is rotated, the cam sleeve is rotated in unison with the control ring, causing the holding rings 5, 6 to axially move with the pins 7, 8 along the intersections of the cam grooves 4a, 4b and the straight grooves 3a, 3b.
In the conventional lens barrel, the distance adjustment between the film plane in the camera and the movement reference position of the second lens group 10 (so-called "back focus" adjustment) is made by inserting a washer 2 between the fixing sleeve 3 and the mount member 1. At the time of assembly, therefore, the distance between the film plane and the second lens group must be measured, and a washer whose thickness is equal to the deviation from the true distance must be selected for insertion. It follows that the tightening and fixing operation of the mount member must be repeated as many times. Thus, the improper arrangement due to the possible range of variation of the tightening force, the degree of complication of the work, the influence of time-consuming work on the cost of assembly, and the preparation of a wide variety of washers of different thickness because tolerances of the individual parts result in many problems.
Reference is made to prior application Japanese Open Utility model No. Sho 53-54655 which is relevant to the above-identified field of art.
FIG. 3 shows an embodiment described in said Utility Model No. Sho 53-54655. This embodiment comprises an inner sleeve 11 of certain length in which first to fourth lens cells are movably fitted in spaced relation to one another; a stop ring 13 is mounted at the front end of the inner sleeve to hold a distance adjusting ring 12; a cam sleeve 14 is fitted on the outer periphery of the inner sleeve 11 to control the relative position of the above-described lens group; play gaps, t, for adjustment are arranged on the inner sleeve 11 at the front and rear of the cam sleeve; thrust rings 15, 16 are rotated onto the threaded end portion 14a to fix the above-described cam sleeve 14 in position; finally, the rear end of the inner sleeve is fixed to a support tubular body 17 of the lens barrel.
The above-described parts are assembled so that the cam sleeve 14 is brought into engagement with the inner sleeve 11, then moved to effect adjustment to a predetermined position relative to the barrel body 17, then the thrust rings 15, 16 are rotated to axially move to the left and right for tightening purposes so that the position of the cam sleeve 14 relative to the inner sleeve 11 is adjusted, and then the thrust rings 15, 16 and cam sleeve 14 are fastened to the inner sleeve 11, by set screws 18, 19.
The above-described invention makes use of thrust rings 15, 16 and set screws 18, 19 as the means for fixing the cam sleeve 14 to the inner sleeve 11 and covers its outer periphery with a distance adjusting sleeve 12.
The zoom lens mounting device according to the above-described invention has, among others, a disadvantage in that the number of parts is large. Another disadvantage is that the distance adjustment of the cam sleeve 14 must be performed by repeating the tightening and loosening operation of the thrust rings 15, 16, and the set screws 18, 19.